Can they get them?
Just because I know Kovu gets super stressed every time I do a water change. When I put him back in his tank he's a little pale and has a dark horizontal stripe in the middle of him =o Or is this something else?

I think the same thing happens to my betta. I noticed it yesterday when I was changing the water. I saw a line and he was lighter.

On the other hand, my coworkers and I decided to give our bettas "play dates" for a few minutes yesterday and brought their fishies next to my betta tank. My coworker wanted her betta to stretch his fins to see how they look because they are all curled and bent. When they the bettas flared they all got darker and brighter! It was very pretty.

Yep!! They can and do! I have a male that is more stressy then my females!!! If I give him a salt bath or remove him for any reason, BOOM stress stripes. So, I just medicate him in his tank from now on.